1. Field of the Invention
The present general inventive concept relates to an LED package having improved light efficiency, a display panel, and an illumination system and a projection system employing the LED package.
2. Description of the Related Art
A projection system forms images on a display panel using light emitted from a light source, magnifies and projects the images on a screen through a projection lens unit such that a viewer demand for a large-scale screen can be met. The projection system can use a lamp as the light source. However, the lamp has disadvantages of a big size, an expensive manufacturing price per unit, intense heat emission, and a short life expectancy.
Accordingly, the projection system can use a laser or a light-emitting diode (LED) as the light source instead of the lamp. The LED is advantageous, because it is inexpensive and has a long life expectancy. However, a large number of LEDs are required, because a brightness of a single LED is not sufficient to project the images.
FIG. 1 is a plan view illustrating a conventional LED package 10 used in a projection system. As illustrated in FIG. 1, a plurality of LED chips 15 are arranged at a predetermined interval on an LED substrate 13 in the conventional LED package 10. The LED chips 15 each have a shape that is roughly square. A DMD (Deformable Mirror Device), which is a type of display panel that forms images in the projection system, forms the images using a two-dimensional arrangement of a plurality of micromirrors by independently operating each micromirror.
FIG. 2A is a view illustrating an incident light Li, an effective light Le, an out-of-range light Lo, and an ineffective light Lu provided according to rotational movements of a micromirror 30 when the DMD is used as the display panel to form the images in the projection system. When the micromirror 30 is in an on or an off state, a path of each light beam is illustrated in FIG. 2A after the incident light Li is reflected by the micromirror 30. For example, the display panel, which has an aspect ratio of about 16:9, may be about 2.3 cm in width and about 1 cm in length. The micromirror 30 disposed inside the display panel is extremely small. A size of the micromirror 30 is on a μm (micrometer) scale and it is difficult to precisely control an operation of the micromirror 30. A rotational angle of the micromirror 30 is limited by a structure of the DMD and a cone angle of the incident light is limited by a slant angle a of the micromirror 30.
When the micromirror 30 is in the on-state, the incident light Li is incident on the micromirror 30 at an incident angle a so that the incident light Li may be reflected from the micromirror 30 and progress toward the screen in a perpendicular direction. When the micromirror 30 is in the on-state, light used for forming the images after the incident light Li is reflected from the micromirror 30 is represented by the effective light Le. When the micromirror 30 is in the off-state, light propagating outside of a projection lens unit after the incident light Li is reflected from the micromirror 30 is represented by the ineffective light Lu. A cone angle of the incident light Li needs to be within +a so that the effective light Le and the incident light Li do not interfere with each other. For example, the cone angle of the incident light Li may be within ±12° when a is 12°. Next, the micromirror 30 is tilted to an opposite side and the incident light Li is reflected toward a direction deviated from a vertical axis (i.e., along which the effective light Le is reflected in the on state) when the micromirror 30 is in the off-state. A window 31 covers the micromirror 30 and the out-of-range light Lo is reflected from the window 31.
As mentioned above, the cone angle of the incident light Li is limited to ±a so that the incident light Li and the effective light Le do not interfere with each other. FIG. 2B is a plan view illustrating the incident light Li, the effective light Le, the out-of-range light Lo, and the ineffective light Lu projected onto the same plane surface in order to explain a relationship between a rotational axis C of the micromirror 30 and the effective light Le. The rotational axis C is perpendicular to a first axis X and parallel to a second axis Y with regard to the cone angle illustrated in FIG. 2A. The cone angle of the second axis Y has enough margin compared with the first axis X, because, as illustrated in FIG. 2B, the incident light Li and the effective light Le may interfere with each other along the first axis X, but do not interfere along the second axis Y. Accordingly, it is possible to improve light efficiency by making the cone angle of the second axis Y greater than that of the first axis X. An elliptical light beam can be made using a stop to increase the cone angle of the second axis Y in the projection lens unit.
FIG. 3A is a plan view illustrating a structure of a display panel 35 having the micromirrors 30 arranged in two-dimensions, and a relationship between the rotational axis C of the micromirror 30 and the display panel 35. FIG. 3B is a plan view illustrating a comparison of light 40 illuminated from the conventional LED package effective light 42 formed by the stop of the projection lens unit. The rotational axis C corresponds to the second axis Y. When comparing the illuminated light 40 to the effective light 42 (Le), there is problem in that the light efficiency is deteriorated by the stop that removes a large portion of the illuminated light 40 as illustrated in FIG. 3B, because the incident light Li incident on the display panel 35 has a square distribution in a structure of the conventional LED package, as illustrated in FIG. 1.